Just to add to what Dennis explained very well.
The HWH air leveling system will first level the coach side to side, then front to back. It will repeat those two steps till the coach is level or the air bags run out of adjustment.
The first step the HWH does in leveling is to release air to achieve level. There are sensors on the air bag manifold that will allow the air pressure to only go so low. Those sensor setpoints are unique to each coach manufacturer. So, what that means is the HWH brain will not let the coach sit on the frame when leveling.
If, and only if, the HWH brain cannot level the coach by exhausting air, then it will cause the aux compressor to come on and the brain will inflate air bags to raise a side or end of the coach.
Because the HWH brain exhausts air first, you will find on almost all cases that the step is as low to the ground as it can be for the site you are parked on. Much lower than a jack based system.
You can override the system and manually level if you choose.
And to repeat what others have said, the HWH air leveling system does NOT work like the HWH hydraulic jack system.